(1) Field of the Invention
This invention relates to kerfed gypsum board having improved strength along the kerfed edge, and relates to a process providing the kerfing.
(2) Description of the Prior Art
Kerfing boards or panels is not new to the construction industry. Accordingly, providing kerfed edge gypsum board for wall and ceiling construction is well established. In such panels, the kerfing comprises a slot running the length of the edges, usually two opposite edges, and provides an engageable conformation for some type of stud, clip, runner, or other flanged supportive device inserted within the kerf. These flanged supportive members are usually constructed from steel and other metal alloys which provide strength and rigidity to a wall or ceiling system. Edge strength is therefore desirable to provide secure retentive connections between the gypsum board and supporting structure.
Edge strengthening in kerfed gypsum board has been attempted in various manners. Generally, gypsum board panels having kerfed edges also have some type of hardening or strengthening agent localized in the kerfed outer edge portion. Such hardening or strengthening is widely known to the gypsum board industry and can be accomplished by numerous methods, such as addition of sugar solutions or other hardening materials along the outer edge portions during board formation at the manufacturing plant. Another method of strengthening kerfed edge board involves multiple layering wherein a gypsum core is covered along opposing faces by a metal or wood sheathing. In this construction the kerfing is most beneficially provided within the sheathing material rather than the gypsum core. Thin laminates, such as paper or plastic, are sometimes utilized as board coverings. With a thinner laminate the gypsum core is kerfed and the coating material adds some additional strength at the board edge.
In all the above-described typical kerfed edge gypsum board, kerfing is accomplished through mechanical sawing. Saw cutting involves circular saws contacting edges of board as the board moves down a conveyor or the like. The typical kerfing of gypsum board provides parallel sidewalls joined by a smooth bottom surface generally disposed at right angles to the sidewalls. When a wood panel or sheathing is specially kerfed a tongue-and-groove connection may be provided. In this manner the tongues and grooves have bevelled or inclined sidewalls which incline toward one another. This is provided by positioning the conventional circular saw apparatus to incline inwardly to cut these converging sidewalls. Other wood panel grooving can be done by planers or shapers well known to the woodworking art. The tongue and groove connection is directly panel-to-panel and no flanged support is utilized. Also, the groove bottom surface connecting the sidewalls is a flat plane.
Alterations of conventional mechanical sawing techniques have occurred in attempts to provide enhanced strength for the kerfed edge of gypsum board. The nature of saw cutting is such that it generates extreme vibration within the gypsum core and creates weakened fracture planes that erodes the strength of the gypsum attained during setting. Even though various alignments and positions for mechanical saw cutters have been tried, they generate deleterious side efforts. The addition of sugar solutions or other hardening additives to the board edge have aided in providing an edge which partially overcomes this weakening. However, it would be desirable to provide kerfed edge gypsum board having strength greater than that provided by conventionally saw cut edges, even where gypsum hardening chemicals have been administered to the conventionally saw kerfed edge.
The building construction industry uses kerfed gypsum board multifariously. Many wall and ceiling designs require demountability to provide accessible and replaceable panel elements in these systems. The need for strength along the kerfed edges of these boards is clear. Because the supportive members are generally rigid and are typically comprised of steel or other metal alloy, much abuse is given to the board edge in sustaining these demountable attachments. Providing enhanced edge strength has been an industry-wide, long felt need.
The conventional mechanical saw cutting of kerfs for gypsum board also creates considerable dust problems at the manufacturing plant. It prohibits doing a desirable preliminary step of predecorating the gypsum board prior to cutting. Typical coatings are plastics such as rigid, or plasticized, polyvinyl chloride film and polyethylene film. Prefinished gypsum board panels may not be cleanly kerfed due to the static electric clinging of finely comminuted gypsum produced by the saw cut. It is therefore desirable that a prefinished gypsum board undergo kerfing without the need for either cleaning the panel, or providing the film overlay at a later stage.
The industry has a long felt need for a gypsum board having enhanced kerfed edge strength for utilization with kerf engaging flanged supports. A process to provide such strength has been sought as well. Additionally, it has been an industry-wide need to provide a dustless process to allow for prefinishing, with plastic coating or the like, of gypsum board prior to kerfing the edge.
(3) Objects of the Invention
It is a primary object of this invention to provide a gypsum board having at least one kerfed edge which provides improved strength for retention by flanged support members at the kerfed portions.
It is also a major object of this invention to provide a process for kerfing gypsum board which provides improved edge strength at the kerfed portion.
It is further an additional object of this invention to provide a dustless kerfing process for gypsum board.
It is also an object of this invention to provide a process which allows the prefinishing of a gypsum board, with plastic coating or the like, prior to the kerfing step.
It is an additional object of this invention to simultaneously kerf two opposite edges of a gypum board.
It is an important object of this invention to provide a kerfed edge gypsum board whereby the kerf is cut by a pair of pressurized streams of aqueous liquid inclined inwardly toward one another into the edge of the gypsum board at a pressure sufficient to cut to a depth of from about one-quarter inch to about three-quarters inches.
A related object of this invention is to provide a kerfed edge gypsum board having a kerf with inclined sidewalls inclined toward one another but do not intersect and are joined by an uneven jagged bottom surface which is the characterizing effect created by the application of a pair of pressurized streams of aqueous liquid projected into the board edge.
A concomitant objective of this invention is to provide gypsum board having a thickness of from about one-half inch to about one inch with increased edge strength along kerfed portions thereof.